BPF : arch/x86/net/bpf_jit_comp.c : fix wrong condition code in jit compiler

[PATCH] BPF : arch/x86/net/bpf_jit_comp.c : fix wrong condition code in jit compiler

Posted by zyf 1 year, 4 months ago

change 'case BPF_ALU64 | BPF_END | BPF_FROM_LE' to 'case BPF_ALU64 | BPF_END | BPF_FROM_BE'

Signed-off-by: zyf <zhouyangfan20s@ict.ac.cn>
---
 arch/x86/net/bpf_jit_comp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 06b080b61aa5..7f954d76b3a6 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1786,7 +1786,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
 			break;
 
 		case BPF_ALU | BPF_END | BPF_FROM_BE:
-		case BPF_ALU64 | BPF_END | BPF_FROM_LE:
+		case BPF_ALU64 | BPF_END | BPF_FROM_BE:
 			switch (imm32) {
 			case 16:
 				/* Emit 'ror %ax, 8' to swap lower 2 bytes */
-- 
2.39.2

Re: [PATCH] BPF : arch/x86/net/bpf_jit_comp.c : fix wrong condition code in jit compiler

Posted by Daniel Borkmann 1 year, 4 months ago

On 9/25/24 10:23 AM, zyf wrote:
> change 'case BPF_ALU64 | BPF_END | BPF_FROM_LE' to 'case BPF_ALU64 | BPF_END | BPF_FROM_BE'
>
> Signed-off-by: zyf <zhouyangfan20s@ict.ac.cn>
> ---
>   arch/x86/net/bpf_jit_comp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 06b080b61aa5..7f954d76b3a6 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -1786,7 +1786,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
>   			break;
>   
>   		case BPF_ALU | BPF_END | BPF_FROM_BE:
> -		case BPF_ALU64 | BPF_END | BPF_FROM_LE:
> +		case BPF_ALU64 | BPF_END | BPF_FROM_BE:
>   			switch (imm32) {
>   			case 16:
>   				/* Emit 'ror %ax, 8' to swap lower 2 bytes */
Please elaborate on the exact issue you've encountered. Right now it looks
like you did this change just based on code review but not based on a real
world bug?

BPF_ALU64 | BPF_END | BPF_FROM_LE instruction is unconditonal swap,
see also commit 0845c3db7bf5c4ceb ("bpf: Support new unconditional bswap 
instruction").
As it stands your change additionally breaks BPF selftests.